This invention relates to luminaires, specifically to those for use in lighting situations in which it is not desired to achieve equal lighting at all positions illuminated by the luminaire. By the term `luminaire` is meant an apparatus which distributes, filters and/or transforms light from one or more lamps mounted in the apparatus.
It is known that in some lighting situations it is desired not to light uniformly the complete surroundings to a luminaire, but to direct the light in particular directions, for example the luminaire for a street light specifically directs in a downwards direction most of the light emitted by the lamp. The distribution of the light is fixed by the luminaire.
In some situations the fixed light distribution does not prove to be a problem. There are, however, lighting situations, such as in a subway, where a luminaire of fixed light distribution may result in either a large wastage of light to ensure that all the area is adequately illuminated, which in a subway results in a higher than necessary degree of illumination of the walls and certain parts of the floor surface, or it may result in inadequate lighting of the entire area but not wastage of light.
Theoretically it would be possible individually to manufacture each luminaire so as to give the light distribution best suited to the proposed position in which the luminaire is to be mounted. This option, however, is not feasible economically.
It is known to manufacture luminaires with two reflectors of which each can swivel relative to a fixed lamp, to vary the distribution of illumination. It is also known to vary the distribution of illumination by moving the light source relative to the reflectors.
Neither of these options gives a very satisfactory range of light distribution.